package NC4_判断链表中是否有环;


class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
        next = null;
    }
}
public class Solution {
    public boolean hasCycle(ListNode head) {
        ListNode fast = head;
        ListNode slow = head;

        if (head == null || head.next == null){
            return false;
        }
        while (fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;

            if (fast == slow){
                return true;
            }
        }
        return false;
    }
}